Sharesies (New Zealand)
Sharesies is ideal for those who only want to invest small amounts each week/month (less than $1,000). Fees are higher than other big brokerages but are reasonable. This is the platform I've been using for my demo portfolio on Instagram. If you use this link to sign up, you will get a free $5 credit in your account to get you started!
CommSec Pocket (Australia)
I didn't find many good options for small investors in Australia. The best I found was CommSec Pocket which lets you invest in various index funds for $2 brokerage up to $1,000. It's not perfect but it's reasonable if you keep investment amounts large and infrequent.
If you're investing larger amounts you can use the regular CommSec platform.
Raiz is a micro investing platform in Australia that lets you automatically invest spare change into various funds. You can also set up regular contributions and make lump sum contributions, and get cash backs for shopping at a wide range of retailers. It is a pretty cool passive investing app, although the fees are on the higher side ($2.75/mth).
You can get a free $5 credit in your account if you sign up using this link.
eToro is a do-it-all investing platform that offers various financial products. It operates internationally, has low fees and is quite popular. It has a lot of instruments so might be overwhelming for new investors.
Revolut is a neobank which is great as a regular bank account but also lets you invest in US stocks commission free.
Trade Republic (Germany)
Trade Republic is an zero commission investing app based out of Germany.
DEGIRO is a European broker that operates in most countries in the EU. The fees are okay, but it does allow you to invest in a good amount of ETF index funds commission free.
Acorns is a passive "set-and-forget" investing app that invests your spare change and also gives you cash back on purchases. It has a monthly fee (starting at $1) but is good for those who want to passively build a portfolio without thinking about it.
Cash App (US)
Cash app is a popular banking and payments app owned by Square. It has an investing function that allows you to easily start investing in stocks and Bitcoin. You can get started for as little as $1.
Note: The only platforms I can vouch for personally are Sharesies, Asb Sec, Raiz and nabtrade. I have never used any of the others. They are suggestions only. Do your own research.